Selecting Pneumatic Linear Slides

8/9/2019 Selecting Pneumatic Linear Slides

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Apneumatic linear slide combines an air cylinderpower source with a guide mechanism thatsupports the workload over a precise linear path.Tey can perorm tasks as simple as a pressingoperation, or as demanding as multi-axis robotics.

What Force is required - determines air cylinderbore size

Load capacity required - determines size andbearing type o the slide guide mechanism

Stroke required - total linear distance traveled Operating speed - cycles per minute and/or

inches per second

By utilizing the slide manuacturers EngineeringData provided or each model series, much engi-

neering time can be saved. Data in this article willbe expressed in US Customary units o pounds andinches.

Force

By using the ormula Force = PSI x Area (poweractor), the linear slides cylinder bore is deter-mined. Note that many slide models have a differ-ent power actor or the extend and retract stroke(actor considers area lost by the piston rod). I theapplication involves pressing, such as an assemblyoperation, consider the possibility that more orcemay eventually be required than initially expected.A preventative solution is to size to a larger boreand regulating it to a lower supply pressure. Tispressure can then be increased when required, toincrease the slides output orce. Another method oincreasing slides output without sizing to a modelwith a larger bore is to utilize a tandem cylinder orMulti-Power option. (Multi-Power is a registeredtrademark o Fabco-Air, Inc.)

Lifing applications require that the slide have atleast twice the output orce as the weight to be

lifed. Underpowered slides that just barely lifthe load will operate poorly, with a slow, jerky, andun-controlled motion.

Finally, many applications require very little orce,and bore size is ofen mistakenly ignored. Selecta slide with a bore size that provides a sufficient

volume o air to operate with a smooth, controlledmotion. Avoid excessively large bores that waste airneedlessly, and thereby waste energy.

FABCO-AIR www.fabco-air.com phone 1-352-373-3578

Figure 1 shows the top view o one style o linearslide that could be used in a pressing application.Te guide mechanism consists o a bearing blockwith two guide shafs attached to a common tool

bar. Below, two linear slides have been combinedto orm a two axis slide. Figure 1A.

Selecting Pneumatic Linear Slidesfor Automated Assembly Equipment

Selecting Pneumatic Linear Slidesfor Automated Assembly Equipment

Guide Shaft

Bearing Block

Air Cylinder

Tool bar

Figure 1

odays equipment designer can choose rom a widearray o Linear Slide models offered in the market-place, but how does one decide which model bestsuits the application?

Slide Selection

Selecting a linear slide involves several basic actors,including:

Figure 1A


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S e l e c t i n g l i n e a r s l i d e s f o r a u t o m a t i o n a s s e m b l y e q u i p m e n t

Load Capacity

A slide must support a workload over the lengtho the linear motion within the limits o precisionrequired by the application. A linear slide carryinga paddle that knocks boxes off o a conveyor doesnot need the same degree o precision as a partsplacer on an Assembly Machine. Because o thesewide variances in application requirements, theengineering data pertaining to the slides loadcapacity will indicate sae loading in pounds andpredict the amount o toolbar deflection, orbending, in thousandths o an inch.

Te largest category o linear slides common

today employ two or more shafs as the guidingmechanism. Most workloads are attached to thereciprocating toolbar, producing an overhung load.Te load capacity is ultimately determined by twoactors - the strength o the guideshaf to resistdeflection, and the ability o the linear bearing tosupport that load. Although overhung workloadsproduce undesirable loading to the leading edgeo the linear bearing, most bearings have a muchhigher load rating than the strength o the guide-shafs (to resist deflection).

Note that a slide with linear ball bearings may berated or 20 pounds with .005 deflection in anoverhung load situation, and yet the our bearingsmay have a combined load rating o several hun-dred pounds. Tis bearing over-capacity assuresprecision and long lie even in overhung loadingsituations.

Linear bearings, whether ball bearings or sleevetype bearings, will support the highest loads whenthat load is applied over the entire length o the

Figure 2B shows a stationary slide with a loadplate attached to reciprocating guide shafs.


Slide Motion

Load

Figure 2A

Stationary Cylinder

Load Motion

Load

Figure 2B

Flange Nuts

Threaded Rod

Toolbar

Rear Stop Bar

Figure 3

Stroke

Slides are commonly offered in 1.0" stroke incre-ments. Designers generally will speciy a strokeslightly longer than the application requires, andutilize optional adjustable stops. Tese hard stopswill repeat within +/- .001" stopping accuracy.

bearing(s). Tis is commonly known as a carriageload. wo styles o carriage loads are show here.Figure 2A shows a load attached to a mountingplate on the reciprocating slide.

Heavy loads, such as shuttling a toggle press ora rivet unit between two work locations, wouldbest be handled with a linear slide configured as

a carriage. Note that a carriage load slide with ashort stroke can carry several hundred pounds oworkload.

Another element actored into a linear slides loadcapacity is the bore and stroke. Obviously, a linearslide with a load capacity o 200 pounds would beo no use i it were powered by a 1/2" bore cylinderthat produced only 10 or 15 pounds o thrust. Bythe same token, a 30" stroke slide with small 1/4"diameter guideshafs would not have sufficientstrength to be o any practical value. Pre-Engi-neered linear slide packages take into account

the need to balance out load capacity versus orceavailable.

Stop options may consist o clamp collars or athreaded stop bolt / stop nut arrangement shownhere in Figure 3.


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Linear slide operating speed

An ofen overlooked aspect is speed. It can bedifficult to obtain accurate speed inormation, yetignoring speed actors can have disastrous results.A sae speed range or a pneumatic linear slidewithout external stops is generally 6 to 8 inchesper second. A 12" stroke in 2 seconds is ap-proximately 6" per second. It is approximate speedbecause acceleration and deceleration time has notbeen taken into account. On shorter strokes,ignoring acceleration/deceleration can be very

misleading. A 1.0" stroke in 0.16 seconds is an

average speed of 6" per second, but in reality,

nal speed is much higher because a good por-

tion of time was spent accelerating. High speeds

develop severe impact forces when stopped sud-

denly at end of stroke. Urethane bumpers, either

within the cylinder or external, can be used to

cushion these forces if stopping accuracy is not an

issue. Adjustable stops in conjunction with either

hydraulic shock absorbers or optional internal

cylinder air cushions can be employed to provide acushioned, precision stop.

Bearing type and speed are also related. Highspeeds are best accomplished with linear ball

bearings, which can travel up to 100" per second.Short stroke, ast-reciprocating motions shouldavoid ball bearings. Te inertia o the ball circuittends to make the balls skid in their tracks whendirection is reversed suddenly.

Options

Options allow the designer to custom tailor thelinear slide to suit the application. Tese includetoolbar and toolplate styles, bearing type, adjust-able stops, shock pads, air cushions or hydraulicshock absorbers, and importantly, sensor options.

Sensors are the interace between the linear slideand the electronic controller. Sensing options aremany, and include reed or Hall Effect switchesactuated by a magnetic piston band on the slidesair cylinder. Many slide models offer a proxim-ity switch option operated by a moving targeton the slides motion. Mechanical snap action

switches and air pilot switches, as well as LVDlinear transducers may also be available.

Saves time and money

Packaged pneumatic linear slides will save costsat every step. Free CAD files are readily available,and can be inserted directly into the design, savingnumerous engineering hours. Build time and re-lated costs are reduced when using an off-the-shellinear slide component. Maintenance and machine

repair costs are lowered by the use of standard,

rather than custom components. Even items likemachine manuals and parts lists are simplied

when component assemblies such as linear slides

are incorporated into the equipment.



Retract shockabsorber

Extend shock absorber

Proximity switch

Limit switchactuator andhousing

Adjustable extendstroke stop collar

Prox. switchactuator

Adjustable shock dog

Typical options shown on a Model SE linear slide


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Brief linear slide history

Powered linear slides can trace their origins tothe dawn of the Industrial Age when a lead screw

was added to the primitive lathes of the time to

power the tool post carriage. Later, mechanical

cams were developed to power slides and provide

a programmed motion. Wooden gun stocks were

mass-produced from a master pattern with special

machinery utilizing cam-operated linear slides.

Air cylinder and hydraulic slides evolved in the

early Twentieth Century. Although these powered

slides were reliable and cost-effective, the relay

logic control systems available at the time were

complicated, trouble-prone, and lacked exibility.

Any change in sequencing required re-design and

re-wiring.

Today, programmable controllers are used to

control the sequencing of air powered linear

slides. This leap in technology has revolutionized

modern industrial equipment. Equipment costs

and lead times have been reduced. Small volume

consumer products can now be automated. The

ability to easily re-program gives manufacturers

the exibility to offer custom tailored products.

Need something special?

Not that many years ago, air powered linear slides

were not available as a packaged component,

as were used to today. Slides were individu-

ally designed and fabricated by the equipment

builder, who used a combination of purchased

components, such as air cylinder, coupler, bear-

ings, and shafting, and custom machined blocks,

plates, or weldments. This custom component was

expensive, but performed exactly as the designer

intended.

Packaged linear slides became available to meet

the demands of machine designers/builders who

didnt want to re-invent the wheel every time a

linear motion was required. The advantages and

cost savings were self evident, and a new category

of pneumatic component emerged.

But what about the times that an off-the-shelf

slide product wont quite t your application? You

may be in need of a special slide.

A special might be something as simple as a

custom sensor, or custom mounting holes and

Carriage Motion

LoadCenter Support

Figure 4A

Carriage Motion

Load

Figure 4B

dowels. These are modications that would be

difcult to do after the slide is assembled, so it is

best left to the slides manufacturer to add thesefeatures for you. A special part number will be

assigned, making ordering andre-ordering very

easy.

A completely new custom slide may be in order.

Who better to design, test and manufacture that

slide than the experts who build thousands of

them. A call to the Applications Department

could save you a lot of time, money, and

aggravation.

Center support adds load capacity

Carriage loads applied to guideshaft style linear

slides can cause the shafts to deect, or bend,

especially on longer strokes. Figures 4 A and B

show optional center support members attached

to guideshafts which dramatically increases load

carrying capacity. By attaching the shaft support

at the center, deection can typically be reduced

to less than .005", even on very heavy loads.

Rather than sizing up to a slide model with very

large diameter guideshafts, you may be able to use

a smaller model with the addition of the optional

center support.

Safe Loading charts are usually included in slide

manufacturers literature. The charts aid your

design considerations by predicting maximum

deections at various strokes and loads.



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TS Series (Linear ball bearings)Very compact. It is the only linear ballbearing slide available that is built intothe air cylinder.

EZ Series (Linear ball bearings)

Rugged slide with guide shafs either sideo integral air cylinder. Te bearings arespaced urther apart as stroke increases,providing exceptional bearing support.

L & S Series (Sleeve bearings)An inexpensive series using non-repairableair cylinders. Te L Series is similar to theEZ Series while the S Series is similar tothe SE. Note: Sleeve bearings need clear-ance to operate. Tereore some toolbarplay exists. L & S slides are not intendedor ultra-precision applications.

SE Series (Linear ball bearings)A shortened version o the EZ Series to savelength. Cylinder is built into the bearing blockwhich houses our linear ball bearings.

GB Series (sleeve bearings)

Air cylinder is machined into bearing block.

Standard eatures include bottom, side & rearmounting holes, top & side ports. oolbarwith top, ront, and bottom mounting holes.

Reasons to select: Rugged block slide, eaturing replace-able Duralonbearings, repairable built-in cylinder,

interchangeable bolt pattern. Dual port locations,multiple mounting suraces. en inch stroke or less.

Reasons to select: Used or applications where the extremeprecision o a linear ball bearing slide is not required.S Series Shorter than L, but less capacity and more play.

L Series high load capacity. Less playthan S because bearings are urther apart.

Reasons to select: Wide spacing of guide shasto resist torsional load. Good load capacity.Provides no-play precision motion. Widestchoice o tooling, stop, and shock options.

Reasons to select: Shorter than EZ. Good loadcapacity. Wide spacing of guide shas to resisttorsional load. Linear ball bearings at each end obearing block provide no-play precision motion.

Reasons to select: Used where space islimited. High load capacity. Linear ballbearings at each end o cylinder provideno-play precision motion. Many toolingoptions available.

Quick reference guide to FABCO-AIR linear slides

since 1958

Fabco has all the popular off-the-shel pneumatic components youwant, ready or immediate shipment. Yet almost hal o our businesscomes rom helping customers solve design problems with specialpneumatic solutions. We can design, prototype and deliver customsamples within 72 hours! Fabco-Air solves problems. Let us help!

With operations housed in 61,000 sq. f. in Gainesville, Florida,Fabco is dedicated to developing and providing advanced fluidpower technology to give our customers the competitive edge theyneed in their field. 24/7 lights-out precision machiningcentersdrive production, assure product quality and enable reliable delivery.

Fabco-Air, Inc. 3716 NE 49th Ave. Gainesville, FL 32609-1699

About Fabco-Air

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Selecting Pneumatic Linear Slides